It has been known that glass fiber-reinforced polypropylene (GFPP) can exhibit improved strength by using aminosilane-treated glass fibers and adding carboxylic acid group-containing polypropylene. It is also known that an acid-modified polyolefin is used for glass fiber treatment. However, studies on the acid-modified polyolefin used have mainly focused on impregnation properties and bundling properties, and the properties of the modified polyolefin-based resin for glass fiber treatment for improving the properties (particularly fatigue strength under oscillation) of GFPP have not been extensively studied (see Patent Documents 1 and 2, for example).
Glass fiber treatment and the composition of a resin composition containing treated glass fibers (glass fiber-reinforced polypropylene) have been studied separately, and only a limited number of studies have been made on the combination of the glass fiber treatment and the composition of the resin composition. Accordingly, outstanding performance has not yet been developed (see Patent Document 3, for example).
Although studies have been made on improvement of fatigue strength under oscillation (see Patent Documents 4 and 5, for example), these studies have mainly focused on the molecular weight of the polypropylene resin part or the like. Specifically, the interface between glass and a resin (particularly polyolefin used for a sizing agent) has not yet been studied.
[Patent Document 1] JP-A-3-181528
[Patent Document 2] JP-A-2003-253563
[Patent Document 3] JP-A-7-309979
[Patent Document 4] JP-A-2004-2837
[Patent Document 5] JP-A-2003-321555
The invention has been achieved in view of the above-mentioned problems. An object of the invention is to provide a modified polypropylene-based resin for glass fiber treatment capable of forming a molded article which exhibits significantly improved fatigue strength under oscillation, a surface-treated glass fiber, and a fiber-reinforced polypropylene-based resin.